Multimedia conferencing systems allow for simultaneous exchange of audio, video and data information among multiple conferencing sites. Systems known as multipoint control units (MCUs) perform switching functions to allow three or more sites to intercommunicate in a conference. The MCU links multiple conferencing sites together by receiving frames of digital signals from the sites, processing the received signals, and retransmitting the processed signals to appropriate sites. The digital signals may include audio, video, data and control information.
The ITU Recommendation T.120 series specifies data protocols for multimedia conferencing to provide conferencing applications such as file transfer, still image exchange and shared whiteboard. The T.120 protocol series includes infrastructure recommendations (network specific transport protocols, T.123; multipoint communications services (MCS), T.122/125; and generic conference control (GCC), T.124) and the application protocols that make use of the infrastructure. The T.120 series provides a data communications service in a multimedia conference. Many types of networks including PSTN, ISDN, CSDN and LAN are supported by the T.120 series.
At the base of the T.120 series infrastructure recommendations is the T.123 transport protocol profile which is specific to the underlying network. This profile provides reliable point-to-point data transport to the MCS layer above.
In a multimedia conference in which the conference sites connect to the MCU over digital links, the fixed bandwidth of the digital link is divided among the media types: video, audio, and data. The more bandwidth dedicated to video, the higher the video quality. Conversely, the more bandwidth dedicated to data, the faster the data transfer for such data applications as file transfer. These allocations between video, audio and data are generally fixed at the time the conference is initiated among the conference sites. While the video rate is generally constant, the data rate tends to be bursty. If the conference is initiated with too low a data bandwidth, data transfers can take too long during the conference. If the data bandwidth is set too high, the data channel may be underutilized for most of the conference with video quality being compromised.
A need exists for a capability that maximizes video quality when data is not being used and minimizes data transfer time when data is being used in a multimedia conference. The present invention provides a conference service capability that dynamically allocates link bandwidth among video, audio and data channels in response to changes in the utilization of those channels.
In accordance with the present invention, a method and apparatus for multimedia conferencing in a multipoint control unit provides dynamic bandwidth allocation among information channels of transmission links connecting plural conference sites to the multipoint control unit. The respective transmission links each have a first information channel and a second information channel with each conference site operable to transmit and receive first information (e.g., video) and second information (e.g., data) signals to and from other conference sites in the respective information channels. For each transmission link a first portion of the link bandwidth is allocated to the first information channel and a second portion is allocated to the second information channel. The MCU monitors the utilization of the second information channels and changes the bandwidth allocation for all of the transmission links in response to changes in the utilization for at least one of the second information channels.
Each information channel comprises inbound (i.e., inbound to the MCU) and outbound (i.e., from the MCU) channels. In a preferred embodiment, the utilization is monitored by measuring the data rate of information signals in the outbound channel and comparing the measured data rate to the allocated information channel bandwidth to determine the channel utilization. In an alternate embodiment, the data rate in the inbound channels can be measured.
The MCU changes the bandwidth allocation by decreasing the first portion allocated to the first information channel and increasing the second portion allocated to the second information channel in equal amounts when the utilization for a number of the second information channels rises above a high utilization threshold. When the utilization for a number of the second information channels drops below a low utilization threshold, the MCU reallocates the link bandwidth by increasing the first portion allocated to the first information channel and decreasing the second portion allocated to the second information channel. In alternate embodiments, utilization of either or both information channels can be monitored.
In an embodiment, the MCU reallocates the link bandwidth by increasing data bandwidth and decreasing video bandwidth when the data channel utilization for a number of the data channels is above the high utilization threshold. The bandwidth is again reallocated in favor of video bandwidth when the data channel utilization for a number of the data channels is below the low utilization threshold. In an alternate embodiment, the MCU inhibits transmission of video signals from the sites when the video bandwidth is decreased. When the bandwidth is reallocated to increase video bandwidth, the MCU uninhibits video transmission from the sites.
In the preferred embodiment, the MCU controls and manages a service policy in which video quality is sacrificed in favor of data transfers to a majority of conference sites while conversely, video quality is favored. over data transfer time for data needs of individual sites.
With the dynamic bandwidth allocation of the present invention provided at an MCU, no changes or upgrades are needed at the endpoint multimedia terminals.